Since 3-oxygermylpropionic acid undergoes polymerization in a complicated manner and is useful for various applications, it has attracted attention of many researchers from the viewpoints of pharmacological activities in recent years. JP-B-63-62492 discloses anti-cataract, as well as other, activities of this compound (The term "JP-B" as used herein means an "examined Japanese patent publication"). Further, it was reported that carboxyethylgermanium sesquioxide, which has been known for a long time and which is generally called Ge132, has a twelve-membered ring structure (J. Am. Chem. Soc., vol. 98(25), pp. 8287 (1976)). However, this compound has some disadvantages. For example, the pharmacological activities thereof vary from lot to lot. In addition, the activities of the compound decrease, for example, due to processing conditions or upon dispensing.
As the maillard reaction inhibitor, the compounds disclosed in JP-B-67827, EP-A-0638075, and the like are known. However, there are demand for new maillard reaction inhibitors which are different from these compounds.
The present inventors have conducted extensive studies on preparation methods whereby the inherent pharmacological activities of 3-oxygermylpropionic acid can be sustained in a stable state. They have further studied the mechanism of action of this compound in vivo. As a result, the inventors discovered various substances that can serve as a stabilizer for 3-oxygermylpropionic acid (JP-A-61-65819 and U.S. Pat. Nos. 4,889,715 and 5,340,806) and the inventors also found that sugars serve to enhance the pharmacological activities thereof (JP-A-60-190714 and U.S. Pat. Nos. 5,336,688 and 5,260,056) (The term "JP-A" as used herein means an "unexamined published Japanese patent application").
The structure of carboxyethylgermanium sesquioxide has already been determined (J. Am. Chem. Soc., vol. 98(25), pp. 8287 (1976)). JP-B-57-53800 suggests the possibility of the existence of various 3-oxygermylpropionic acid compounds. However, these substances each suffers from the above-mentioned problems.